Brian Stokes Mitchell — star of musicals, including “Kiss Me Kate” and “Ragtime” — didn’t pull punches before a New York premiere of “Show Stopper,” a new doc on high-flying producer Garth Drabinsky, who recently served jail time for fraud. “I have very complex feelings about Garth,” Mitchell said at a DGA screening of the Barry Avrich-directed film. “I got to see him at his most awful and selfish, and cruel and heartless . . . But I also got to see him do some incredible things. Through ‘Ragtime,’ he put me on the map. It’s the most magical show I’ve ever done . . . it had this incredible transformative power. So whatever you may think of him, he was an interesting force.” Drabinsky was convicted in Canada in 2009 for cooking the books of his firm, Livent, which had mounted shows, including “Kiss of the Spider Woman.” The disgraced producer was paroled in October after serving a year — including a month in maximum security Millhaven Institution. Others at the screening included Chita Rivera, Rob Reiner, Tovah Feldshuh and The Post’s Michael Riedel, who played emcee. Drabinsky recently produced a feature version of Broadway play “Barrymore” starring Christopher Plummer.